Milbemycin is natural product from microbial source, which can be used as pesticide, and there have been data showing that it is one of the best acaricides in the modern world. The US Environmental Protection Agency identifies it as a low-risk pesticide and Holland approves it as “GNO” (natural product in the production of crops). It belongs to ecology friendly pesticide and is applicable to the comprehensive prevention and control of organic agriculture pests and diseases, and has become a popular insecticidal and acaricidal agent in developed countries.
Milbemycin is a metabolite having insecticidal activity, which was screened from the fermentation broth of microorganism by Sankyo Company Limited of Japan using two-spotted spider mites as tested insects (U.S. Pat. No. 3,950,360). After a lot of fundamental research, the mixture of the components of milbemycin A3 and milbemycin A4 (A3:A4=3:7) was used as an acaricide in 1983. The structures of milbemycin A3 and milbemycin A4 are as shown in formula I. In 1990, 1% of milbemycin emulsifiable concentrate (milbeknock) was used as an acaricide for tea and eggplants in Japan. In 1993, 1% of milbemycin emulsifiable concentrate was also registered in Japan as a pesticide for pears, peaches, watermelons, strawberries, eggplants and flowers. Currently, milbemycin has been registered in many countries, such as Japan and many countries in Europe and America, etc. and is recommended by the US Environmental Protection Agency to be used as a safe, environment friendly insecticidal and acaricidal agent.
Since the fermentation broth containing milbemycin has complex composition and the separation is difficult, milbemycin is usually used and reported as the mixture of A3 and A4 components and the production and use of single component are rarely reported. The main reason is that it is difficult to isolate A3 or A4 single component individually from fermentation broth wherein ratios of A3 and A4 are similar, which affects the final yield. In case of A3, the content of A3 in the fermentation broth is less than 30%. To get A3 single component, a lot of A4 would be lost. Achieving A3 or A4 single component production can further facilitate the application of milbemycin single component in other fields. The most effective way to obtain a single component is to obtain a new strain capable of producing a single component.
